1. Field of the Invention
The present invention relates to a method for producing nickel powder having a large particle size in which the surface is smoothed and the inner part is densified, in a step of blowing hydrogen gas into a nickel ammine sulfate complex solution under high temperatures and high pressures to obtain nickel powder.
2. Description of the Related Art
The use of nickel powder as a functional material and a positive electrode active material of a nickel-hydrogen battery and the like has been advanced, and a method for producing nickel powder using a wet process as a method for producing such nickel powder has been developed.
As a method for producing nickel powder industrially by the wet process, a method for producing nickel powder by adding a reducing agent to reduce nickel from solution has been developed, and especially, a method of reducing nickel using hydrogen gas as a reducing agent is industrially inexpensive and has been widely used.
This method is described as a process for producing nickel powder by “Sherritt Gordon Inc.”, as shown in POWDER METALLURGY, 1958, No. 1/2, P. 40-52. This process includes mixing a complexing agent with a nickel sulfate aqueous solution to form a solution containing a nickel ammine complex, putting the solution in a pressure vessel followed by sealing the vessel, heating the solution to about 150 to 250° C. to obtain saturated vapor pressure, and blowing hydrogen gas into the solution, in which the nickel ammine complex is reduced by hydrogen to obtain nickel powder.
The nickel powder obtained by this method includes uneven particles having voids on the surface thereof. The nickel powder has problems in that, when the powder is shipped as a nickel metal product in the form of powder as it is, the powder produces dust since it has a small particle size; and since the powder has unevenness, it has a low bulk density and requires excess volume when a container is filled with the powder.
The present invention intends to solve the above problems that when nickel powder, which is obtained by adding seed crystals to a nickel ammine complex solution in an autoclave and performing hydrogen reduction reaction under high temperatures and high pressures, is shipped as a nickel metal product in the form of powder as it is, the powder produces dust; and since the powder has unevenness, it has a low bulk density and requires excess volume when a container is filled with the powder. The present invention provides nickel powder which is obtained by adding seed crystals to a nickel ammine complex solution and performing hydrogen reduction reaction under high temperatures and high pressures, wherein the nickel powder does not produce dust during handling, and a container can be efficiently filled with the nickel powder.